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Mercury 289 HiPo specs: 289 ci (4.7L) 8-cylinder, 4.00 x 2.87 in (101.6 x 72.9 mm) bore and stroke, 10.5:1 compression. Rated 271 hp. OHV.
The Mercury 289 HiPo is oversquare — the 4" bore exceeds the 2.8701" stroke by 39.4% — a layout that favors airflow and RPM over leverage at the crank. The 2.8701" stroke does not reach 4,000 ft/min of mean piston speed until about 8,350 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 36.1 ci (592 cc).
10.5:1 on iron heads is in the range that usually runs on pump premium; iron holds heat, so treat it as the less forgiving side of that range.
It is one of 24 engines in the Windsor family, sitting between the 221 ci and 351 ci members. 2 factory variants share these dimensions, rated at 271 hp. Factory fitments include the Mercury Comet, Mercury Cougar, Mercury Comet Cyclone.
| Displacement | 289 ci / 4.7 L |
|---|---|
| Bore | 4" |
| Stroke | 2.8701" |
| Cylinders | 8 |
| Compression ratio | 10.5:1 |
| Bore/stroke ratio | 1.394 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 271 hp |
| Bore/stroke character | 1.394 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,870 ft/min — conservative for a street engine |
| Displacement per cylinder | 36.1 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| — | 271 hp | 289 HiPo |
| — | 271 hp | 289 HiPo, 289 Hi-Po |